A tetrathiafulvalene-perylene diimide conjugate prepared via click chemistry

Article abstract of DOI:10.1016/j.tetlet.2009.07.108

A new tetrathiafulvalene (TTF)-perylene diimide (PDI) conjugate is prepared from an azide-functionalized TTF and an acetylenic PDI employing a Cu(I)-catalyzed Huisgen-Meldal-Sharpless reaction ('click chemistry'). Thus, the TTF donor and PDI acceptor unit

Full text of DOI:10.1016/j.tetlet.2009.07.108

Tetrahedron Letters 50 (2009) 5613–5616
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A tetrathiafulvalene–perylene diimide conjugate prepared via click chemistry
*
Katrine Qvortrup, Michael Åxman Petersen, Tue Hassenkam, Mogens Brøndsted Nielsen
Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark
a r t i c l e i n f o
a b s t r a c t
Article history:
A new tetrathiafulvalene (TTF)–perylene diimide (PDI) conjugate is prepared from an azide-functional-
ized TTF and an acetylenic PDI employing a Cu(I)-catalyzed Huisgen-Meldal-Sharpless reaction (‘click
chemistry’). Thus, the TTF donor and PDI acceptor units are linked together by a 1,2,3-triazole unit.
The molecules are found to assemble on a mica surface, forming fibrilar structures.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 4 June 2009
Revised 7 July 2009
Accepted 17 July 2009
Available online 23 July 2009
Keywords:
Alkynes
Click chemistry
Perylene diimide
Tetrathiafulvalene
Perylene diimides (PDI, Fig. 1) have attracted wide interest as
candidates for organic solar cells and artificial photosynthesis ow-
ing to their high fluorescence quantum yields and thermal chemi-
cal and photochemical persistencies.1 Recent interest has emerged
in preparing donor–acceptor conjugates between PDI and the good
electron donor tetrathiafulvalene (TTF).2 TTF has been widely
exploited as a redox-active unit in both materials and supramolec-
ular chemistries.3 Hudhomme and co-workers2a showed that the
fluorescence emission intensity of the PDI unit can be reversibly
tuned by the oxidation states of the TTF unit. We became inter-
ested in developing a new synthetic route to obtain such dyads
by taking advantage of ready access to the acetylenic PDI 1, re-
cently prepared by us4 and in parallel by Langhals and Obermeier.5
We have shown that this alkyne can be subjected to an oxidative
homo coupling reaction under Glaser-Hay conditions to provide a
PDI dimer,4 while Langhals and Obermeier5 have shown that the
alkyne unit of the PDI can be subjected to the Cu(I)-catalyzed Huis-
gen-Meldal-Sharpless reaction6 (‘click chemistry’) with azides to
furnish triazoles. Click chemistry has also been shown to tolerate
the presence of a TTF unit.7 Here, we explore click chemistry for
successfully linking TTF and PDI units.
hydroxide, and the resulting thiolate was then alkylated by treat-
ment with 2-chloroethanol to provide compound 3. This alcohol
was subsequently treated with diphenylphosphoryl azide (DPPA)
and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in dry N,N-dimeth-
ylformamide (DMF) for 4 h followed by the addition of sodium
azide, which produced the TTF-azide 4.
Next, we subjected the TTF-azide 4 to click reactions in DMF
solution. First, compound 4 was treated with phenylacetylene
and CuSO4/ascorbic acid, generating the Cu(I) catalyst in situ,
which resulted in formation of the TTF-triazole derivative 5 in good
yield (Scheme 2). The same conditions were employed in the reac-
tion between 4 and the PDI-alkyne 1, which furnished the TTF–PDI
dyad 6 as a dark-red solid, isolated in a somewhat lower 31% yield
(Scheme 2). The product was purified by column chromatography
followed by precipitation from dichloromethane by addition of
methanol.
O
N
O
O
N
O
S
S
S
S
H
H
Construction of TTF–PDI dyads from 1 using click chemistry re-
quires an azide-functionalized TTF, the synthesis of which is shown
in Scheme 1. TTF compound 2 containing a cyanoethyl-protected
thiolate group was prepared according to the procedure of Becher
and co-workers.8 Base-promoted elimination of acrylonitrile fol-
lowed by alkylation allows for ready functionalization of the thio-
late. Thus, the cyanoethyl group was removed using cesium
TTF
PDI
O
N
O
O
C6H13
C6H13
N
O
1
* Corresponding author. Tel.: +45 3532 0210; fax: +45 3532 0212.
E-mail address: mbn@kiku.dk (M.B. Nielsen).
Figure 1.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.07.108

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K. Qvortrup et al. / Tetrahedron Letters 50 (2009) 5613–5616
presence of both a donor group and an acceptor group (Fig. 2).
MeS
MeS
SMe
S
S
S
S
Thus, the dyad showed two reversible oxidations at half-wave
potentials E1/2 = +0.08 and +0.40 V versus Fc+/Fc (Fc = ferrocene)
corresponding to two one-electron oxidations of the TTF unit. In
addition, two reversible one-electron PDI reductions were ob-
served at E1/2 = À1.05 and À1.26 V versus Fc+/Fc, which are close
to those observed for other PDI derivatives.4 The dyad showed
characteristic PDI UV–vis absorptions at 458, 489, and 525 nm in
CH2Cl2.
CN
S
2
1) CsOH H2O, MeOH
DMF
68%
2) ClCH2CH2OH
The TTF–PDI 6 was subjected to Atomic Force Microscopy (AFM)
studies on a mica surface. A solution of the dyad was prepared by
dissolving a few micrograms in toluene. A single drop was allowed
to dry on the mica substrate. The dried sample was then studied
using an optical microscope (Fig. 3A). The film formed small wires,
created by the receding solvent during evaporation. An image from
close-up inspection of the wires is displayed in Figure 3B, the
height of the wires is about 30 nm and the width is about 1–
MeS
MeS
SMe
S
S
S
OH
S
S
3
1) DPPA, DBU
DMF
80%
2) NaN3
2 lm. This image and the AFM image of a thin film obtained by
deposition from chloroform (Fig. 3C) reveal that the molecules
form treads lying in a net-like texture. As indicated by the color
coding (Fig. 3C) and the cross-section (Fig. 3D), the treads in the
film have a uniform thickness of about 2 nm. The widths of the
treads are difficult to determine. They seem to range from a few
nanometers up to 10 s of nanometers. However, this is probably
not the true width, since in the image, there is a convolution effect
with the AFM probe tip. The formation of the treads suggests that
there is some loose ordering of the molecules. We speculate that
the PDI section of the molecule controls the packing of the mole-
MeS
MeS
SMe
S
S
S
N3
S
S
4
Scheme 1.
Ph
CuSO4 5H2O
ascorbic acid
N
MeS
MeS
S
S
S
S
S
N
N
4
cules so that one PDI is
p-p stacked with a neighboring PDI. The
DMF
85%
SMe
TTF unit and the alkyl chains would then be connected to the back-
bone of the stacked PDI in more or less disordered packing. The
molecules, standing edge on, would then give rise to the 2 nm thick
wires observed in the AFM image.
In conclusion, we have expanded the synthetic scope of the
acetylenic PDI 1. Thus, click chemistry using this building block
provides a new method for preparing donor–acceptor dyads com-
prised of TTF and PDI units. The molecules assemble into small
wires on a mica surface. Future work will be aimed at exploring
the triazole group as a site for metal ion complexation and not
merely as a synthetically convenient spacer group. Complexation
of a suitable metal ion may provide a triad system for light-induced
charge separation.
Ph
5
1
CuSO4 5H2O
ascorbic acid
DMF
31%
N
MeS
MeS
S
S
S
S
S
N
N
O
N
O
O
N
O
C6H13
C6H13
SMe
6
Scheme 2.
2-(2-Hydroxyethylthio)-3,6,7-tris(methylthio)tetrathiafulvalene (3):
The cyanoethyl-protected TTF thiolate 2 (5.43 g, 12.7 mmol) was
dissolved in dry DMF (250 mL) and argon was passed through the
solution for 0.5 h. An argon-degassed solution of CsOHÁH2O (2.34 g,
TTF–PDI dyad 6 was subjected to cyclic voltammetry studies in
dichloromethane (containing 0.1 m Bu4PF6), which confirmed the
Figure 2. Cyclic voltammogram of TTF–PDI 6 in CH2Cl2 and 0.1 M Bu4PF6. Reference electrode: Ag/Ag+; counter electrode: Pt; working electrode: glassy carbon; scan rate:
0.1 V/s.

K. Qvortrup et al. / Tetrahedron Letters 50 (2009) 5613–5616
5615
Figure 3. Structure of dropcast samples. (A) Optical microscope image showing small wires of TTF–PDI 6, created by the receding of the drop of toluene during evaporation.
(B) AFM image of a single wire. (C) The structure of a film dropcast from a chloroform solution. The white lines in B and C denote the locations of the height profile cross-
sections shown in D and E, respectively.
13.9 mmol) in dry MeOH (30 mL) was added via syringe over
0.5 h. The reaction mixture was stirred for another 0.5 h, then 2-chlo-
roethanol (3.32 mL, 49.5 mmol) was added and stirring was contin-
ued overnight. The mixture was evaporated to dryness, and the
residue was subjected to column chromatography (SiO2, gradient
elution: CH2Cl2 ? CH2Cl2/MeOH, 95:5), affording 3 (3.6 g, 68%) as a
dark-red semi-solid. 1H NMR (300 MHz, CDCl3): d = 2.39 (s, 6H,
2ÂSCH3), 2.43 (s, 3H, SCH3), 2.52 (br s t, J = ca. 6 Hz, 1H, CH2OH),
2.91 (t, J = 5.9 Hz, 2H, SCH2), 3.69 (br s dt, J = 5.9 Hz, ca. 6 Hz, 2H,
CH2OH); 13C NMR (75 MHz, CDCl3): d = 19.3 (two overlapping), 19.4,
39.3, 60.1, 110.3, 111.7, 122.7, 127.5, 127.7, 133.4; MS (FAB): m/z
418 [M+]; HRMS (FAB): found: m/z 417.8795 [M+], C11H14OS8
requires: m/z 417.8810.
(2 mL) at rt, after which CuSO4Á5H2O (3.0 mg, 0.012 mmol) and
ascorbic acid (4.2 mg, 0.024 mmol) were added. The solution was
stirred at rt for 12 h followed by evaporation of the solvent in vacuo.
Column chromatography (SiO2, CH2Cl2 followed by 5% v/v MeOH in
CH2Cl2) gave the product 5 as an orange solid (100 mg, 85%). Mp
113–114.5 °C. 1H NMR (300 MHz, CDCl3): d = 2.43 (s, 6H, 2 Â SCH3),
2.48 (s, 3H, SCH3), 3.33 (t, J = 6.6 Hz, 2H, SCH2), 4.62 (t, J = 6.6 Hz, 2H,
CH2N), 7.34 (m, 1H, Ph), 7.43 (m, 2H, Ph), 7.84 (m, 2H, Ph), 7.97 (s,
1H, triazole-H); 13C NMR (75 MHz, CDCl3): d = 19.4 (three overlap-
ping), 35.9, 49.9, 109.5, 112.8, 120.6, 121.1, 125.9, 127.6, 127.7,
128.4, 129.0, 130.7, 134.0, 147.9; MS (FAB): m/z 545 [M+]; HRMS
(FAB): found: m/z 544.9328 [M+], C19H19N3S8 requires: m/z
544.9345.
2-(2-Azidoethylthio)-3,6,7-tris(methylthio)tetrathiafulvalene (4):
TTF-alcohol 3 (300 mg, 0.716 mmol) was dissolved in dry DMF
(20 mL), and then diphenyl phosphoryl azide (DPPA) (0.77 mL,
3.58 mmol) was added. The mixture was cooled on an ice bath,
and DBU (0.11 mL, 0.72 mmol) was added. After stirring for 4 h un-
der nitrogen at rt, sodium azide (0.23 g, 3.58 mmol) was added.
The reaction mixture was stirred at rt for another 24 h then
washed with water, and the organic layer dried (Na2SO4), filtered,
and concentrated in vacuo. Column chromatography (SiO2, CH2Cl2)
of the residue afforded 4 (254 mg, 80%) as an orange oil. 1H NMR
(300 MHz, CDCl3): d = 2.43 (s, 6H, 2ÂSCH3), 2.45 (s, 3H, SCH3),
2.95 (t, J = 6.8 Hz, 2H, SCH2), 3.51 (t, J = 6.8 Hz, 2H, CH2N3); 13C
NMR (75 MHz, CDCl3): d = 19.3 (three overlapping), 35.2, 50.8,
110.3, 112.1, 122.3, 127.6, 127.8, 133.1; one overlapping signal;
MS (FAB): m/z 443 [M+]; HRMS (FAB): found: m/z 442.8900 [M+],
C11H13N3S8 requires: m/z 442.8875.
TTF–PDI dyad (6): The TTF-azide 4 (40 mg, 0.090 mmol) and al-
kyne-functionalized PDI 1 (50.0 mg, 0.082 mmol) were dissolved
in DMF (5 mL) at rt to afford a deep-red-colored suspension. Then
CuSO4Á5H2O (1.0 mg, 0.004 mmol) and ascorbic acid (1.4 mg,
0.008 mmol) were added. The mixture was stirred at rt for 12 h, after
which the solvent was removed in vacuo. The crude product was
purified by column chromatography (SiO2, CH2Cl2 followed by 5%
v/v MeOH in CH2Cl2). A red solid was isolated and redissolved in
CH2Cl2 (3 mL). The pure product was precipitated from this solution
by addition of MeOH. TTF–PDI 6 was isolated as a dark-red solid
(27 mg, 31%). Mp >150 °C (decomp.). 1H NMR (300 MHz, CDCl3):
d = 0.83 (t, J = 6.7 Hz, 6H, CH((CH2)5CH3)2), 1.23–1.39 (m, 16H,
CH(CH2(CH2)4CH3)2), 1.84–1.89 and 2.22–2.34 (2Âm, 2Â2H,
CH(CH2(CH2)4CH3)2), 2.36 (s, 3H, SCH3), 2.37 (s, 3H, SCH3), 2.44 (s,
3H, SCH3), 3.26 (t, J = 6.7 Hz, 2H, SCH2), 4.75 (t, J = 6.7 Hz, 2H,
SCH2CH2N), 5.13–5.21 (m, 1H, NCH(C6H13)2), 5.53 (s, 2H, NCH2),
7.93 (s, 1H, triazole-H), 8.29–8.54 (m, 8H, PDI-H); MS (FAB): m/z
1053 [M+H+]; HRMS (FAB): found: m/z 1053.1715 [M+H+],
C51H51O4N5S8 requires: m/z 1053.1707.
2,3,6-Tris(methylthio)-7-[2-(4-phenyl-1H-1,2,3-triazol-1-yl)ethyl-
thio]tetrathiafulvalene (5): TTF-azide 4 (100 mg, 0.23 mmol) and
phenylacetylene (0.03 mL, 0.27 mmol) were dissolved in DMF

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K. Qvortrup et al. / Tetrahedron Letters 50 (2009) 5613–5616
2. (a) Leroy-Lhez, S.; Baffreau, J.; Perrin, L.; Levillain, E.; Allain, M.; Blesa,
Acknowledgment
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The Danish Research Agency is acknowledged for supporting
this work.
Shen, Y. J. Photochem. Photobiol., A: Chem. 2008, 200, 334;
e Jaggi, M.;
Blum, C.; Dupont, N.; Grilj, J.; Liu, S.; Hauser, J.; Hauser, A.; Decurtins, S.
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